diff --git a/src/infra/session-maintenance-warning.test.ts b/src/infra/session-maintenance-warning.test.ts
index 3cf0ee72eeae..7fd1a454d367 100644
--- a/src/infra/session-maintenance-warning.test.ts
+++ b/src/infra/session-maintenance-warning.test.ts
@@ -199,4 +199,37 @@ describe("deliverSessionMaintenanceWarning", () => {
       { sessionKey: params.sessionKey },
     ]);
   });
+
+  it.each([
+    [59_500, "60 seconds", "1 minute"],
+    [3_570_000, "60 minutes", "1 hour"],
+    [86_370_000, "24 hours", "1 day"],
+  ])(
+    "formatDuration rolls over %dms to next unit instead of %s",
+    async (pruneAfterMs, _buggyOutput, expected) => {
+      mocks.deliverOutboundPayloads.mockRejectedValueOnce(new Error("force system event"));
+      const params = createParams({
+        warning: { pruneAfterMs, wouldPrune: true, wouldCap: false, maxEntries: 100 } as never,
+      });
+
+      await deliverSessionMaintenanceWarning(params);
+
+      expect(firstSystemEventCall()?.[0]).toContain(`older than ${expected}`);
+    },
+  );
+
+  it.each([
+    [30_000, "30 seconds"],
+    [1_800_000, "30 minutes"],
+    [43_200_000, "12 hours"],
+  ])("formatDuration keeps %dms in its own unit as %s", async (pruneAfterMs, expected) => {
+    mocks.deliverOutboundPayloads.mockRejectedValueOnce(new Error("force system event"));
+    const params = createParams({
+      warning: { pruneAfterMs, wouldPrune: true, wouldCap: false, maxEntries: 100 } as never,
+    });
+
+    await deliverSessionMaintenanceWarning(params);
+
+    expect(firstSystemEventCall()?.[0]).toContain(`older than ${expected}`);
+  });
 });
diff --git a/src/infra/session-maintenance-warning.ts b/src/infra/session-maintenance-warning.ts
index 5871de1311c3..9248de3d5f1c 100644
--- a/src/infra/session-maintenance-warning.ts
+++ b/src/infra/session-maintenance-warning.ts
@@ -54,20 +54,20 @@ function buildWarningContext(params: WarningParams): string {
 }
 
 function formatDuration(ms: number): string {
-  if (ms >= 86_400_000) {
-    const days = Math.round(ms / 86_400_000);
-    return `${days} day${days === 1 ? "" : "s"}`;
+  const secs = Math.round(ms / 1000);
+  if (secs < 60) {
+    return `${secs} second${secs === 1 ? "" : "s"}`;
   }
-  if (ms >= 3_600_000) {
-    const hours = Math.round(ms / 3_600_000);
-    return `${hours} hour${hours === 1 ? "" : "s"}`;
-  }
-  if (ms >= 60_000) {
-    const mins = Math.round(ms / 60_000);
+  const mins = Math.round(secs / 60);
+  if (mins < 60) {
     return `${mins} minute${mins === 1 ? "" : "s"}`;
   }
-  const secs = Math.round(ms / 1000);
-  return `${secs} second${secs === 1 ? "" : "s"}`;
+  const hours = Math.round(mins / 60);
+  if (hours < 24) {
+    return `${hours} hour${hours === 1 ? "" : "s"}`;
+  }
+  const days = Math.round(hours / 24);
+  return `${days} day${days === 1 ? "" : "s"}`;
 }
 
 function buildWarningText(warning: SessionMaintenanceWarning): string {